A machine of this type is for example intended for a gas treatment process such as the extraction, separation, storage or transport of gas, in particular of natural gas, in some cases comprising hydrogen sulphide (H2S).
High-power rotating electrical machines comprise on the stator, and optionally on the rotor if this is not provided with permanent magnets, coils for the flow of electric current for generating a magnetic flux. Similarly, windings of this type are used in magnetic bearings, allowing shafts to be supported in rotation, in particular shafts of alternators, motors, compressors.
In a gas treatment machine of this type, the rotating electrical machines and the magnetic bearings are cooled by the gas used in the treatment process. The coils are therefore in contact with this gas, which in certain cases, in particular when it contains hydrogen sulphide, may be aggressive and corrosive towards these coils, in particular in a damp environment. In other words, the rotating electrical machines and magnetic bearings are located in a particularly aggressive and corrosive environment.
The coils used in these conditions are formed from a copper conductor covered with an insulator such as polyimide. The copper conductor insulated in this manner is rolled up to form a coil. These coils are shaped, and then the winding formed in this manner is covered with insulating tape, which forms a secondary insulation generally known as ground insulation. This ground insulation is generally formed from a polyimide, epoxy, polyester-mica or glass-mica tape.
The straight parts of the coils which are wrapped in this manner are polymerised, and then the coils are mounted within the structure of the rotating machine, after which this rotating machine is placed in a heat chamber where the windings are impregnated by a thermosetting material, such as epoxy, the polymerisation of this thermosetting material taking place at a temperature of approximately 110° C. to 160° C.
It has been found that over time, the corrosive environment in which the rotating electrical machines or magnetic bearings operate leads to deterioration of the coils.